The present invention relates to an improvement in a bearing apparatus for use in various kinds of rotary equipment such as a spindle motor (which is also referred to as SPM) which is applied to, for example, a hard disk drive apparatus (which is also referred to as HDD) or a video cassette recorder (which is also referred to as VCR).
The present invention relates to a rolling bearing and a bearing apparatus for use in a small-sized motor which is used mainly in information equipment and home appliances.
The present invention relates to a reduction not only in the vibrations and noises, but also to a reduction in the dynamic friction torque of the bearing apparatus which is used to support a motor shaft such as a spindle provided in a HDD and a drum spindle provided in a VCR.
The present invention relates to a ball bearing and a bearing apparatus for a small-sized motor which is used in a HDD, a VCR, or a laser beam printer (which is also referred to as an LBP).
Conventionally, a bearing apparatus, as shown in FIG. 44, comprises a pair of bearings 100 and 100 combined together. The combining direction of the two bearings is not fixed specifically but, generally, the opening sides 201 of the respective retainers 200 of the two bearings 100 and 100, in which dust is easy to occur, are disposed opposite to each other, whereby the bearings 100 and 100 are disposed as a bearing unit which can reduce the generation of dust to the outside of the bearing unit. In FIG. 44, reference character 300 designates a shaft and 400 stands for a spacer which is interposed between the two bearings 100 and 100.
Also, as shown in FIG. 45, there is generally known a bearing with a shaft in which double-row raceway 301 and 301 are formed directly in the shaft 300, and a spring 500 is interposed between two outer rings 101 and 101. In this structure, the crown-shaped retainers 200 are incorporated in such a direction that, similarly to the structure shown in FIG. 44, their respective retainer opening sides 202 are opposed to each other. In FIGS. 44 and 45, arrow marks respectively show preload directions. Today, in order to enhance the oscillation resistance (which is also referred to as fretting resistance) of the bearing in transit, a bearing lubricant is filled into the raceways of the bearing, instead of a related method in which the lubricant is filled onto the retainer.
However, when the bearing apparatus of this type is rotated, since the lubricant (a grease as a representative example) is filled in the raceways, the rotation torque of the bearing apparatus and variations in such rotation torque are large. Further, the vibrations of the bearing apparatus not synchronous with the rotation of the bearing apparatus (which is also referred to as NRRO) are also large.
Now, FIG. 46 is an enlarged view of a retainer incorporated into the related bearing apparatus shown in FIG. 45. That is, in such related structure, grease G collecting in the counter-contact-angle side of the outer ring 101 is involved with the rotational movement of a ball 600 and is thereby moved in the rotation (about its own axis) direction of the ball 600. The grease G is scraped by the crown-shaped retainer 200. The thus scraped grease G collects into the outside diameter portion of the retainer end face side (pocket counter-opening side) 202 to provide a collection of grease. The grease collection is contacted with grease G on the outer ring 101 side to thereby generate large resistance, so that the rotation torque of the bearing apparatus increases. Also, the grease G, which has been scraped once, is easy to be involved with the rotational movement of the ball 600, which causes the rotation torque to be unstable and large.
By the way, in the case of an HDD spindle motor for use in information equipment, as shown in FIGS. 47 and 48, a hub 730 is rotatably supported on the periphery of a shaft 720 by a pair of rolling bearings 700 and 700 disposed with a space between them. One end of the shaft 720 is fixed to the central portion of a fixing plate 740 which is referred to as a housing. The rolling bearings 700 and 700 are interposed between the outer peripheral surfaces of the base end portion (in FIG. 47, the lower end portion) and leading end portion (in FIG. 47, the upper end portion) of the shaft 720, so that the hub 730 can be rotated on the periphery of the shaft 720. A stator 750 is fixed to the portion of the middle portion outer peripheral surface of the shaft 720 that is held by the pair of rolling bearings 700 and 700; a rotor is fixed to the portion of the middle portion inner peripheral surface of the hub 730 that is opposed to the outer peripheral surface of the stator 750; and, the stator 750 and rotor 760 cooperate together in constituting an electric motor 770 which is used to drive or rotate the hub 730. Also, a plurality of hard disks 780, 780 is fixed to the outer peripheral surface of the hub 730. By the way, reference characters 790, 790 respectively designate heads for reading records from the hard disks 780, 780 and writing records into the hard disks 780, 780.
On the other hand, the two rolling bearings 700 and 700 respectively comprise inner rings 701 and 701 having inner raceways 701a and 701a formed in the outer peripheral surfaces thereof, outer rings 702 and 702 having outer raceways 702a and 702a formed in the inner outer peripheral surfaces thereof, a plurality of rolling elements 703, 703 rotatably interposed between the inner raceways 701a, 701a and outer raceways 702a, 702a, and crown-shaped retainers 704 made of synthetic resin.
Also, between the outer peripheral surfaces of the axial-direction two end portions of the respective inner rings 701 and 701 and the inner peripheral surfaces of the two end portions of the respective outer rings 702 and 702, there are interposed a pair of seal rings 705 and 705 each of which is formed in a circular ring to thereby close spaces between the inner ring and outer ring peripheral surfaces. The upper and lower bearings are combined together in such a manner that, in order to reduce dust generation to the outside of the bearings, the pocket-opening sides 704a and 704a of the crown-shaped retainers 704 and 704 of the bearings are opposed to each other.
Further, into spaces 706 defined by and between the pair of seal rings 705 and 705, there is filled grease 707 and 707 from one of the pocket-opening sides (in FIG. 47, in the case of the upper rolling bearing 700 the lower-end pocket-opening side; and, also in FIG. 47, in the case of the lower rolling bearing 700, the upper-end pocket-opening side) of the respective spaces 706 and 706. Of the pair of seal rings 705 and 705, at least the seal ring 705 on the grease 707 filling side is to be mounted into a given portion after completion of the grease filling operation.
After the seal rings 705 and 705 are mounted, the seal rings 705 and 705 prevent the grease 707 filled in the respective spaces 706 and 706 from leaking therefrom to the outside.
However, in the above related bearing apparatus, there are still found problems to be solved: that is, when it is rotated, the rotation torque thereof and variations in the rotation torque are large; and vibrations not synchronous with the rotation of the bearing apparatus are also large.
In view of the above, in order to solve the above problems found in the related bearing apparatus, the present inventors have previously proposed a bearing apparatus (Japanese Patent Application 2001-209387) structured such that a bearing incorporating a crown-shaped retainer is fixed to a shaft, wherein a preload is applied to the retainer pocket-opening side of the inner ring of the bearing, and also to the retainer counter-pocket-opening side of the outer ring of the bearing. In this case, it is required that the pocket-opening side and counter-pocket-opening side of the retainer incorporated into the bearing be distinguishable from each other simply and positively from the outside. Especially, in the case of a related bearing with seal plates respectively mounted on two ends thereof, the pocket-opening side and counter-pocket-opening side of the retainer of the bearing, that is, the incorporating direction of the retainer, cannot be distinguished from each other.
By the way, for a motor shaft which is used to drive a hard disk apparatus or a floppy disk apparatus for use in a personal computer and a word processor, there is used a ball bearing having a small diameter. In the case of a ball bearing, as a type for guiding a retainer made of synthetic resin, there are known a rolling element guide type for guiding a retainer using a rolling element (a ball), and an inner ring or outer ring guide type for guiding a retainer using an inner ring or an outer ring. In either of these guide types, as time passes, the quantity of lubricant (grease, or an oil component) filled into the pocket of the retainer decreases, so that the frictional torque of the bearing gradually decreases and becomes almost constant.
As the shape of the pocket of the retainer for holding a ball, there are known two kinds of shapes: that is, as shown in FIGS. 49 and 50, which is an enlarged section view taken along the line VI—VI shown in FIG. 49, one type of retainer pocket shape is such that the inner wall of the pocket 840P of a retainer 840 for holding a ball 830 interposed between an outer ring 810 and an inner ring 820 has a flat cylindrical surface; and, as shown in FIGS. 51 and 52, which is an enlarged section view taken along the line VIII—VIII shown in FIG. 51, the other type of retainer pocket shape is such that the inner wall of the pocket 841P of a retainer 841 has a spherical surface. Further, most of the retainers of an inner ring or outer ring guide type include a cylindrical-shaped pocket, whereas most of the retainers of a rolling element guide type include a spherical-shaped pocket. Also, depending on the situation, there may be taken means in which, as disclosed in JP-A-9-317774, there are formed fine undulations (raised and recessed portions) on the sliding surfaces of these retainers to thereby enhance the lubricating property of the retainers.
On the other hand, when these bearings are used in the above-mentioned motor, in order to enhance the rotation accuracy thereof, generally, two bearings are combined together as a pair and are given a preload.
As described above, in the case of the ball bearing, preferably, when the quantity of the lubricant filled into the pocket of the retainer gradually decreases from the beginning, the ball bearing may be stabilized and the frictional torque of the ball bearing may be constant.
However, in a retainer of an inner ring 820 (or outer ring 810) guide type, including a cylindrical-shaped pocket 840P shown in FIGS. 49 and 50, most of the lubricants circulate in the order of ball surface-raceway surface-pocket surface-ball surface and are left within the pocket. Due to this, the friction torque of the bearing is large when compared with a bearing of a rolling element guide type including a spherical-shaped retainer pocket, which raises a problem to be solved. That is, in the case of a bearing including a retainer of a race guide type including a cylindrical-shaped pocket, since a ball is contacted with the center of the pocket, there does not occur a scraping operation for scraping away the lubricants. Thus even as the time passes, in most cases, the torque of the bearing does not lower.
On the other hand, in the retainer 841 of a rolling element guide type shown in FIGS. 51 and 52, extra lubricants G sticking to the surface of the ball 830 are scraped away by the edge portion of the spherical-surface pocket 841P and are stuck to the inner or outer peripheral surface of the retainer to thereby have no influence on the torque of the bearing; and, the viscous resistance of the lubricant with respect to the ball and race contact portion decreases as the rotation time passes and the reduction of the torque continues.
And, in the case where the scraping operation advances excessively due to the high-speed rotation, cutting of an oil film occurs in the pocket edge portion and ball surface to cause poor lubrication. And due to poor lubrication, there are produced strange sounds. Also, in order to prevent such poor lubrication, the sliding surface of the retainer is set not flat or smooth but is set so as to have desired roughness to thereby form lubricating oil standing portions and thus prevent cutting of the oil film, whereby the friction of the retainer can be controlled for a long period of time. However, in the case of a bearing using such a retainer, similarly to the above-mentioned retainer including a cylindrical-shaped pocket, there is found a problem that the friction torque of the bearing is large.
Conventionally, as means for supporting various rotary parts, for example, there is widely used such a ball bearing as disclosed in JP-A-10-159855 (see FIG. 54).
This ball bearing comprises an outer ring 3 having an outer raceway formed in the inner peripheral surface thereof, an inner ring 2 having an inner raceway formed in the outer peripheral surface thereof, a crown-shaped retainer 5 interposed between the outer and inner rings 3 and 2 in such a manner that it can be rotated with respect to the outer and inner rings 3 and 2, and a plurality of balls 4 respectively rotatably held in a plurality of pockets 5d formed in the crown-shaped retainer 5. The outer peripheral edges 9a of two circular-ring-shaped shield plates 9 are respectively secured to the inner peripheral surfaces of the two end portions of the outer ring 3. The two shield plates 9 prevent grease existing in the above-mentioned ball installation portions from leaking to the outside, and also prevent dust floating on the outside from flowing into the ball installation portions.
As described above, the plurality of balls 4 are rotatably held by the retainer 5. Conventionally, as the retainer 5, for example, there is used a crown-shaped retainer as shown in FIG. 37. This crown-shaped retainer 5 has the same number of spherically-concave-surface pockets 5d as the balls 4 in order to hold the balls 4 in a freely rollable manner. Further, the radius of curvature of the spherically concave surface of the retainer pocket is set slightly larger than the radius of curvature of each of the balls 4.
When the bearing of this type is used to support various rotary apparatuses, generally, two bearings 1 and 1 of this type are used in combination.
However, in the above-mentioned related bearing, there are still found the following problems to be solved.
Recently, as the rotation speed of the rotary apparatus increases, there increases the need for a reduction in the noises and vibrations of the bearing. Also, there is a need for a reduction in the dynamic friction torque of the bearing. However, the related bearing apparatus has become more and more difficult to meet such reduction needs. That is, to reduce the noises and vibrations, the pocket diameter of the retainer 5 may be reduced to reduce the play of the retainer 5 with respect to the ball 4, thereby controlling the movement of the retainer 5. However, when the play (clearance) of the retainer 5 is reduced, there is increased the shearing resistance of lubricants existing between the retainer pockets 5d and balls 4, with the result that the dynamic friction torque of the bearing apparatus increases.
By the way, conventionally, a ball bearing to be incorporated into the above-mentioned HDD, VCR or LBP, for example, as shown in FIG. 44, is composed of a pair of bearings 100 and 100 combined together; and, the combining direction of the two bearings 100 and 100 is not fixed to any specific direction but, generally, the two bearings 100 and 100 are disposed in such a manner that the pocket-opening sides 201 of the respective retainers 200 of the two bearings 100 and 100 are opposed to each other, thereby reducing generation of dust to the outside of the bearings 100 as a training unit.
Also, today, in order to enhance the oscillation resistance (which is also referred to as the fretting resistance) of the product (ball bearing) in transit, a lubricant is filled into raceways formed in the two bearings. Such a configuration is different from a related lubricant filling system in which the lubricant is filled on to the retainers of the two bearings.
However, in the bearing apparatus of this type, there is still found a problem: that is, when it is rotated, since the lubricant is sealed in the grooves of the two bearings, the rotation torque of the apparatus and the variations of the rotation torque are large. Additionally, vibrations not synchronous with the rotation (NRRO) of the apparatus are large.
Also, when the two bearings 1, 1 are used under high-speed rotation, in order to restrict the mechanical slippage of the interior portion of the bearing, it has been considered effective to reduce a contact angle at which the balls and the raceway surfaces are contacted with each other.
However, recently, as the rotation speed of the various rotary apparatus increases, there has been increased the need for a reduction in the dynamic friction torque of the bearing. That is, simply by reducing the contact angle in the above-described manner, the dynamic friction torque of the bearing caused by the high-speed rotation of the bearing can not be restricted sufficiently.
Specifically, the high-speed rotation of the bearing causes the grease existing in the interior of the bearing to move much and, especially, the grease moved to the inside diameter of the outer ring—due to a centrifugal force—is stirred between the outer ring inside diameter and the outside diameter portion of the retainer, thereby increasing stirring resistance or shearing resistance, with the result being that the dynamic friction torque of the bearing is increased.